Generally, the present invention relates to a method and apparatus for mixing air and fuel in an engine of an automobile. More particularly, the present invention relates to a method and apparatus for estimating air-mass inflow into cylinders based on a current throttle setting and also to controlling the amount of fuel input into cylinders based on the estimated air-mass.
Gasoline engines generate power by burning fuel in a combustion chamber. A throttle valve regulates the power output of such gasoline engines. The throttle valve controls the amount of air drawn into the engine. The fuel injected into the engines depends on the amount of air-mass drawn into the engine. Therefore, in order to control the amount of fuel injected into the engine, the amount of air-mass drawn into the combustion chamber must be detected.
Commonly, to detect the amount of air-mass drawn into an engine a Manifold Absolute Pressure (MAP) sensor is used. A MAP sensor detects the pressure and temperature in an intake-manifold and converts the value to an air-mass valve.
FIG. 1 shows a graph illustrating how an output signal of a MAP sensor changes according to throttle valve position changes. Typically, as in FIG. 1, when a throttle valve is operated the pressure in an intake-manifold changes accordingly. As a consequence, the air-mass drawn into a combustion chamber through the intake-manifold also changes accordingly. Therefore, calculation of an appropriate amount of fuel to be injected into a cylinder at each fuel injection period becomes difficult. This results in an excess of noxious exhaust gas because of improper and incomplete burning of the fuel.
In the conventional system, in order to cope with such a situation, (1) a change rate of each of the throttle opening and the intake-manifold pressure is calculated, (2) a first fuel correction value is calculated when the change rate of the throttle opening is greater than a first predetermined value, (3) a second fuel correction value is calculated when the change rate of the intake-manifold pressure becomes greater than a second predetermined value, and (4) such first and second fuel correction values are added to a base amount of fuel calculated based on air-temperature, engine speed, and a throttle setting.
However, a correction formula, for calculating fuel amount correction values, must be established with respect to each of the throttle opening change rates and the intake-manifold pressure change rate. Furthermore, a method for calculating the appropriate amount of fuel must be altered to adopt the established correction formula because newly adopting the correction formula may affect each of the throttle opening dependency, engine speed dependency, and air temperature dependency in an original formula for calculating the amount of fuel.
To appropriately adopt the consequent changes, a lot of experimentation is required. In turn, the experimentation substantially increases the time and cost involved in developing an appropriate engine control method. This experimentation also must be performed for each engine under investigation. Furthermore, the system does not take into consideration and change as the engine ages and the tolerances with the engine change.
One of the principal factors that result in complex relations between parameters for correcting the amount of fuel injected into the cylinders is the temporal discrepancy. The temporal discrepancy occurs between a moment at which an intake-manifold pressure is detected and a moment that the correspondingly injected fuel becomes mixed with the air and together is drawn into the combustion chambers.
FIG. 2 shows a typical period required for the injected fuel to become mixed with air and drawn into the combustion chambers. A temporal discrepancy typically lasts for one cycle of crankshaft rotation. This period occurs between a moment when an intake-manifold pressure is detected and a corresponding fuel amount is calculated and a moment that the injected fuel gets into the combustion chamber for burning. Therefore, under an abrupt change of the throttle opening, such as under hard acceleration or deceleration, precise control of the fuel is very difficult according to the conventional system.
The information disclosed in this Background of the Invention section is only for enhancement of understanding of the background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art that is already known to a person skilled in the art.
The present invention provides for estimating the air-mass drawn into cylinders at an actual point of being drawn into the cylinders. An exemplary system for estimating cylinder intake air-mass of the present invention includes a throttle opening detector for detecting a throttle setting. An engine speed detector for detecting the engine speed and an intake-manifold pressure detector for detecting intake-manifold pressure. Further included is an intake air temperature detector for detecting the temperature of the air drawn into an intake manifold and an electronic control unit for calculating air-mass drawn in to cylinders based on signals of the throttle opening detector, the engine speed detector, the intake-manifold pressure detector, and the intake air temperature detector. Also, the electronic control unit is programmed to execute instructions for an exemplary method for estimating air-mass drawn into cylinders.
An exemplary method for estimating the air-mass drawn into cylinders includes detecting a current throttle opening TPS and detecting a current engine speed RPM. Detecting an air mass Mmani currently drawn into an intake-manifold and calculating a delay period xcex94t from injecting fuel to a predetermined target moment. Calculating an expectation value E_TPSxcex94t of a throttle opening after the delay period xcex94t and an expectation value E_Mmani,xcex94t of air-mass drawn into the intake-manifold after the delay period xcex94t on the basis of the expectation value E_TPSxcex94t of throttle opening. Further included are steps of calculating an expectation value E_Pmani,xcex94t of the intake-manifold pressure after the delay period xcex94t on the basis of the expectation value E_Mmani,xcex94t of air-mass drawn into the intake-manifold and calculating an expectation value E_Mcyl,xcex94t of air-mass drawn into cylinders after the delay period xcex94t on the basis of the expectation value E_Pmani,xcex94t.
In a further embodiment, the calculating expectation value E_TPSxcex94t of the throttle opening calculates the expectation value E_TPSxcex94t on the basis of Newton""s difference method to a predetermined order difference term.
In another further embodiment, the calculating expectation value E_TPSxcex94t of throttle opening includes calculating a first order difference DTPS of the throttle opening and calculating a second order difference xcex94DTPS of the throttle opening. Calculating the expectation value E_TPSxcex94t of the throttle opening on the basis of the equation             E_TPS              Δ        ⁢                  xe2x80x83                ⁢        t              =          TPS      +                        DTPS                      δ            ⁢                          xe2x80x83                        ⁢            t                          xc3x97        Δ        ⁢                  xe2x80x83                ⁢        t            +                        1          2                ⁢                  xe2x80x83                ⁢                              Δ            ⁢                          xe2x80x83                        ⁢            DTPS                                              (                              δ                ⁢                                  xe2x80x83                                ⁢                t                            )                        2                          xc3x97                              (                          Δ              ⁢                              xe2x80x83                            ⁢              t                        )                    2                      ,
wherein xcex4t denotes a time period between detecting moments of a current and a previous throttle openings TPS and TPSprec.
In a yet another further embodiment, the calculating expectation value E_Mmani,xcex94t of air-mass drawn into the intake-manifold includes calculating a base mass Mbase,xcex94t passing through the throttle valve on the basis of an engine speed RPM and the expectation value E_TPSxcex94t of throttle opening. Detecting an air temperature Tin drawn into the intake-manifold and calculating a correction coefficient CT corresponding to the intake air temperature Tin. Calculating a correction coefficient CP corresponding to a pressure ratio of pressure before and after the throttle valve after the delay time xcex94t. Also, calculating the expectation value E_Mmani,xcex94t of air-mass drawn into the intake-manifold by modifying the base mass Mbase,xcex94t based on the correction coefficients CT and CP.
In a still further embodiment, the calculating a correction coefficient CT calculates the correction coefficient CT as a value of             T      0                      T        0            +              T        in            
on the basis of a predetermined temperature T0 and the intake air temperature Tin.
In another still further embodiment, the calculating of a correction coefficient CP corresponding to a pressure ratio includes calculating a temporary expectation value E_Mtemp of air-mass drawn into the intake-manifold after the delay period xcex94t by extrapolation. Further included is the steps of calculating an expectation value E_PTH,xcex94t of pressure before the throttle valve on the basis of the temporary expectation value E_Mtemp and calculating an expectation value E_Ptemp of pressure in the intake-manifold after the delay time xcex94t by extrapolation.
In yet another further embodiment, the calculating of a correction coefficient CP corresponding to a pressure ratio calculates the correction coefficient CP on the basis of a function which monotonically decreases above a threshold pressure ratio and converges to 0 at a predetermined pressure ratio.
In still yet another further embodiment, the calculating of an expectation value E_Pmani,xcex94t of intake-manifold pressure after the delay period xcex94t includes detecting a current intake-manifold pressure Pmani and calculating intake-manifold pressure change xcex94Pmani as a value of xe2x80x9c(E_Mmani,xcex94txe2x88x92Mmani)xc3x97Rxc3x97Tin /Vs.xe2x80x9d Further included is the step of calculating the expectation value E_Pmani,xcex94t of the intake-manifold pressure by adding the detected current intake-manifold pressure Pmani and the pressure change xcex94Pmani.
In a yet another further embodiment, the calculating expectation value E_Mcyl,xcex94t of cylinder intake air-mass calculates the expectation value E_Mcyl,xcex94t of cylinder intake air-mass as a value of the equation E_Mcyl,xcex94t=K(RPM)xc3x97E_Pmani,xcex94t+Prig(RPM), wherein Prig(RPM) and K(RPM) are predetermined functions of engine speed RPM.
An exemplary fuel control system of an engine of the present invention includes a throttle opening detector for detecting the throttle opening or setting and an engine speed detector for detecting the engine speed. Further included is an intake-manifold pressure detector for detecting intake-manifold pressure and an intake air temperature detector for detecting the temperature of the air drawn into the intake manifold and injectors for injecting fuel into the engine. An electronic control unit for calculating the amount of fuel to be injected into the cylinder is based on signals of the throttle opening detector, the engine speed detector, the intake-manifold pressure detector, and the intake air temperature detector. Furthermore, the electronic control unit drives the fuel injectors based on the calculated fuel amount, wherein the electronic control unit is programmed to execute instructions for an exemplary fuel control method of an engine described below.
An exemplary fuel control method of an engine of the present invention includes determining if a predetermined condition is satisfied and estimating an expectation value E_Mcyl,xcex94t of cylinder intake air-mass after the delay period xcex94t according to an exemplary method for estimating air-mass drawn into cylinders described above. Further steps include calculating a fuel amount based on the estimated expectation value E_Mcyl,xcex94t and driving fuel injectors based on the calculated fuel amount.
In a further embodiment, the predetermined condition is satisfied when an interval has passed after starting the engine and there is no malfunctioning of a throttle opening detector, an engine speed detector, an intake-manifold pressure detector, or an intake air temperature detector. Furthermore, the change rate of the throttle opening is greater than a first predetermined change rate, and the change rate of the intake-manifold pressure is greater than a second predetermined change rate.
It is preferable that the further steps of determining if a difference between the estimated expectation value E_Mcyl,xcex94t and a current air-mass drawn into the intake-manifold Mmani is greater than a predetermined value is included. Also, when the difference is greater than a predetermined value, the calculating of the amount of fuel is based on the estimated expectation value E_Mcyl,xcex94t.